1. Field of the Invention
The present invention relates to a horizontal deflection circuit designed to reduce the amount of unwanted radiation of electric fields generated from a CRT (cathode ray tube) and, in particular, from CRTs used for a computer display.
2. Description of the Related Art
In recent years, in displays for computers, decreasing unwanted radiation of an electric field or a magnetic field radiated from the display has become an important subject because there is the possibility that the unwanted radiation thereof is injurious to the health of a user. This object has heretofore been attained by performing electrostatic shielding or electromagnetic shielding using a metallic member for the chassis of the display, as disclosed by Onoe et al in JPA 61-42684, for example. Moreover, in order to reduce the unwanted radiation of the electric field, such technology has also been developed that a transparent conductive layer is provided on a front surface of the Braun tube (CRT) to perform the electrostatic shielding.
On the other hand, as for the method of reducing the unwanted radiation itself from the display, by paying attention to the fact that the unwanted radiation from a horizontal deflection circuit is mainly due to flyback pulses having very high voltage of a single polarity induced in the horizontal deflection circuit, a system of the horizontal deflection circuit which does not generate flyback pulses has been proposed. For example, Wakazono proposed a new scanning system in JP-A-53-133333 which is designed in such a way that the retrace of each sweep cycle is performed in the same period of time as that of the sweep in the forward direction, the beam for carrying the video information arranged in the forward direction is deflected during the sweep in the forward direction, and the beam for carrying the video signals arranged in the reverse direction is deflected during the retrace period. According to this new system, the occurrence of the flyback voltage due to the rapid retrace can be prevented to decrease the unwanted radiation of the electric field. And Kawafuchi et al disclose a deflection circuit using sinusoidal waves to eliminate flyback pulses in JPA3-72783.
However, in the prior art shielding methods, there arise serious problems that both the weight and cost increase because of the use of the metallic member, and it takes too much time for production since trial and error is required for the optimal design. In addition, in the system by Wakazono, there arises a problem that a large-scale circuit which is different in structure from the prior art CRT is required.